Effect of oxide dopants on densification, microstructure and mechanical properties of alumina-silicon carbide nanocomposite ceramics prepared by pressureless sintering

The densification behaviour, microstructural development and mechanical properties of a 5 vol.% silicon carbide dispersed alumina nanocomposite were studied by incorporating six different oxide dopants (1 wt.%). It was found that MgO, Y₂O₃ and CeO₂ enhanced the densification of the nanocomposite, which can be explained by a liquid phase assisted sintering process. The yttria-doped nanocomposite could be pressureless sintered at 1550 °C. Doping with MgO or CeO₂ refines the grain size of the matrix alumina whereas yttria addition induces exaggerated grain growth. The Young's modulus, hardness, fracture toughness and erosive wear resistance were evaluated. Doped nanocomposites exhibit slightly lower Young's modulus and higher hardness values than that of the undoped nanocomposite. CeO₂ doping improves hardness and fracture toughness slightly whereas the improvement in erosive wear resistance was 2.5 times higher than the other nanocomposites. Improvements in properties are explained in terms of residual compressive stresses, grain refinement and grain boundary strengthening.